On their plane ride from San Antonio to Miami on Monday morning, the Heat’s players had momentum and home-court advantage, and there was a very real belief that a third consecutive championship was only three victories away.

The return trip to Texas will have a decidedly different feel.

After losing a pair of games at home in the NBA Finals, the Heat now must win three consecutive games to accomplish its dynastic goal.

Of all the magic this team has conjured in its past three postseasons, a comeback from a 3-1 series deficit to these revenge-driven San Antonio Spurs would be the biggest trick of all. No team has ever come back from down 3-1 to win an NBA Finals.

In Game 3, the Spurs simply couldn’t miss. In Game 4 on Thursday night, the Heat simply looked ready for the offseason.

For the second consecutive game, the Spurs ran laps around the two-time defending champions in the first half. But this time, the Heat didn’t even give chase. It ended in a 107-86 victory for the Spurs, who now stand just one victory from their fifth championship of the Tim Duncan era. The first title was in 1999.

“I don’t think any of us were expecting this type of performance,” Heat coach Erik Spoelstra said of Miami’s lethargic ways.

Game 5 of the Finals is Sunday night at San Antonio’s AT&T Center.

“The focus is winning one more,” Duncan said.

A dunk by Duncan gave the Spurs a 21-point lead in the third quarter, and, following a missed three-point attempt by Ray Allen, Spurs forward Kawhi Leonard answered with a demoralizing three-pointer of his own to make it Spurs 73, Heat 49. The Heat called timeout with 3:48 left in the period, and Spurs reserve Patty Mills ran onto the court waving a towel in celebration.

“They smashed us — two straight home games,” LeBron James said. “They were much better than us. It’s that simple.”

Either in protest of Mills’ celebration or just in objection to Miami’s poor play, fans began booing as the Heat walked to its bench.

The Heat did a lot of walking on this night.

“Maybe we deserved it,” Chris Bosh said of the booing.

The Heat began showing signs of fatigue during the first quarter. By the fourth, Dwyane Wade was simply losing his dribble in transition for turnovers.

No one looked particularly sharp for the Heat, but Wade’s struggles were pronounced. He finished 3 of 13 from the field for 10 points and was subbed out of the game with five minutes to play.

“I’m a very accurate shooter,” Wade said. “I don’t like missing.”

James finished with 28 points, going 10 of 17 from the field, 4 of 8 from three-point range and 4 of 6 from the free-throw line. He left the game with the Heat trailing by 22 points with 3:38 remaining and ripped the compression sleeve off his arm in disgust. James gave the Heat a momentary spark in the third quarter with 10 points in four minutes, but the Heat trailed by double digits for the entire second half.

A three-pointer by Allen cut the Spurs’ lead to nine points with 6:27 left in the second quarter. That was the only time in the final 36 minutes of the game that the Spurs’ lead dropped below 10 points.

Leonard led the Spurs in scoring for the second consecutive game, and he now should be considered the frontrunner for Finals MVP. He finished with 20 points, going 7 of 12 from the field and 1 of 3 from three-point range, after scoring 29 points in Game 3. He also had 14 rebounds.

On Tuesday, Leonard was the driving force behind the Spurs handing the Heat its first loss of the postseason at AmericanAirlines Arena. In his encore, Leonard snapped the Heat’s run of 13 consecutive postseason victories after a loss.

The Spurs followed up their shooting clinic on Tuesday by going 40 of 70 from the field (57.1 percent) in Game 4.

“They’re playing beautiful basketball right now,” said Bosh, who finished with just 12 points.

On the boos, Bosh noted: “Life is harsh. … Maybe we deserve it right now.”

“Our main concern is putting our best game forward,” Spoelstra said before the game.

That didn’t happen.

There were many ways to describe statistically the Heat’s ineffectiveness in the first half, but here are the four best, or worst, depending on the perspective:

• Stunningly, the Heat was 4 of 15 inside the paint. Combined, Wade and James were 1 of 7 in the paint and 0 of 4 in the restricted area. That’s right. They missed every layup they attempted in the game’s first two quarters.
• The Heat registered just four assists. The Spurs had three times that many. Put another way, the Heat had 12 field goals in the first half and the Spurs had 12 assists.
• The Heat shot 35.3 percent from the field. It was the second-worst field-goal percentage of any half this season and the seventh-worst of the Big 3 era.
• Wade was 1-of-7 shooting in the first half.